Scientists at Hewlett-Packard have demonstrated that a layer of molecules just three-billionths of a meter thick can help store data during a computing operation without using traditional semiconductors, adding another piece to a portfolio of technology HP is assembling to perhaps one day construct computers that harness the strange effects of quantum mechanics.

In a paper published today in the Journal of Applied Physics, the researchers report that they've built a functioning "crossbar latch"--an electronic switch that can flip a binary 0 to a 1 and vice versa, and preserve the output of that computation for use in subsequent ones--without using the electronic transistors that form the building blocks of today's computers. In addition, the switch, whose key component is just a single layer of molecules thick, can restore weakened electrical signals so the distinction between 0's and 1's stays crisp. The demonstration proves a design HP patented in 2003, and could pave the way for future computers that operate without silicon transistors, which are falling prey to the quantum mechanical effects that govern the subatomic realm as their circuitry shrinks to ever-smaller sizes.

"Nature agrees with our patent," says Phil Kuekes, a senior computer architect in HP Labs' quantum science research group. "We've designed a device that keeps working, and works even better in the atomic scale." The research was funded by the Defense Advanced Research Projects Agency, the military's research and development arm.

The computer industry has for decades relied on the ability to squeeze more electronic circuitry--and therefore computing intelligence--onto ever-smaller devices at lower costs, as an engine of economic growth. But as conventional silicon components reach the nanometer scale, measured in billions of a meter, scientists foresee a time within the next decade or so when the effects of the quantum mechanical laws that govern that realm make further computing advantages hard to realize with traditional materials. For example, a quantum effect called "tunneling" can impair transistors by causing electrons to leak through their gates, throwing off the distinctions between 0's and 1's that computers rely on to perform their logic.

HP's approach, on the other hand, exploits the tunneling effect. Its crossbar latch consists of three criss-crossing platinum and titanium wires joined by a layer of electrically switchable molecules of stearic acid (a fatty acid that also appears in soap, candles, and chocolate) measuring 2.8 nanometers thick. Traditional computers use semiconductor properties to form the "latch" that preserves the output of a computation for later use. "The most important thing is, we didn't use semiconductors to do this," Kuekes says.

James Ellenbogen, a senior principal scientist at Mitre Corp. in McLean, Va., says HP's advance will give molecular electronics designers the ability to eventually string nanoscale elements together to perform extended computations and move information around a system. It eliminates a key barrier to HP's plans to pursue a molecular-scale computer, and could prove less expensive than traditional semiconductor fabrication techniques. "They've knocked down one of the things that was in the way of their strategy, and they've done a very clever and lovely piece of scientific work in the process," he says.

Companies including AT&T, IBM, Intel, and Microsoft are researching the use of nanotechnology or quantum effects to build computers and software. Researchers at the California Institute of Technology, Carnegie Mellon University, Harvard University, Mitre Corp., Rice University, and Yale University are pursuing research related to HP's method.

According to Stan Williams, an HP senior fellow and director of its quantum science research group, the breakthrough boosts current research at the company that aims to combine more complex computing functions with nanoscale memory. "This was the missing piece," Williams says. HP has been researching what it calls "molecular electronics" since 1996, and holds about a dozen patents in the area.